It has hitherto been investigated to increase the recording density and the reproducing density of magnetic recording media used for the foregoing perpendicular recording system. A magnetic recording medium composed of a base material, a 1st magnetic thin layer formed on the surface of the base material, and a 2nd magnetic thin layer formed on the 1st magnetic thin layer, which can record desired data by magnetization in the thickness direction of the 2nd magnetic thin layer, that is, in the perpendicular direction, has now been developed.
The foregoing 1st magnetic thin layer has a role of forming a part of a magnetic pass in the case of magnetizing the 2nd magnetic thin layer and is required to possess a low coercive force and a high permeability as well as a high saturation magnetic flux density. On the other hand, the 2nd magnetic thin layer is required to possess an anisotropy in the perpendicular direction of the layer. As a material meeting the requirement for the 2nd magnetic thin layer, there are cobalt-chromium system alloys such as cobalt-chromium binary alloy and a ternary alloy composed of cobalt, chromium, and a third metal such as rhodium.
On the other hand, permalloy is usually used for the 1st magnetic thin layer but permalloy does not have a sufficient permeability and saturation magnetic flux density. Furthermore, permalloy is inferior in so-called affinity in magnetic properties with the 2nd magnetic thin layer composed of the foregoing cobalt-chromium system alloy. That is, when the 2nd magnetic thin layer composed of the cobalt-chromium system alloy is formed on the 1st magnetic thin layer composed of permalloy having a face centered cubic lattice in the crystal structure, the formation of a hexagonal system in crystal structure of the thin layer of the cobalt-chromium system alloy is obstructed by the influence of the thin layer of permalloy disposed under the cobalt-chromium system alloy thin layer (in particular, owing to the thinness of the 2nd magnetic thin layer), whereby the excellent perpendicular anisotropy, which is a feature of a cobalt-chromium system alloy, cannot sufficiently be attained. Thus, since permalloy is inferior in affinity in magnetic characteristics with a cobalt-chromium system alloy and does not have a sufficiently high permeability and saturation magnetic flux density as described above, the conventional magnetic recording medium having the foregoing layer structure has a fault that even if a cobalt-chromium system alloy having excellent magnetic characteristics is used for the 2nd magnetic thin layer, the excellent properties of the alloy cannot sufficiently be utilized.